Makhashkala, Dagestan (CNN) -- Two children were killed Wednesday when a package they picked up exploded in a market in Makhashkala, the capital of Russia's North Caucasus republic of Dagestan, the government said.

Initial reports attributed the explosion to a suicide bomber. Two others were injured in the blast.

In a separate incident, three policemen were killed and two wounded after unknown assailants opened gun fire on their car in Buinaksk, another city in Dagestan, a spokesman for the local Investigation Committee said, according to the Russian news agency RIA-Novosti.

Russian military offensives targeting an Islamist insurgency in the region have been taking place for years, but have gained greater attention in the United States since the Boston Marathon bombing. The two brothers in the case have ties to Dagestan.